Conducted by researchers at the Sydney-based George Institute for Global Health, the University of Sydney and University of NSW and published in the British Journal of Medicine, the review found only 13 reliable studies that compared paracetamol with placebo for osteoarthritis and low back pain.
For low back pain there were no significant differences between placebo and paracetamol for pain intensity, disability or quality of life.
For osteoarthritis of knee or hip, there was a statistically significant difference in favour of paracetamol for pain in the immediate (less than two weeks) and short (two weeks to three months) term, and for disability in the short term, but not immediate term.
However, while statistically significant, these findings were not considered clinically significant. The researchers explain that on a pain or disability rating scale of 0 to 100, a difference of 9 points is the smallest difference that you would notice. The combined differences found in the studies were less than 4 points.
This doesn't necessarily mean it doesn't work at all – just that it doesn't work better than placebo. And sometimes the placebo 'worked', with improvements of more than the 9 points at which you'd notice a difference!
There were no long-term studies on the effectiveness of paracetamol versus placebo for either condition.
Safety of using paracetamol
The side effects noticed while taking the treatments showed no difference between paracetamol and placebo, and in general both were well tolerated.
Some studies measured liver function, and found that those taking paracetamol were four times more likely to have abnormal results. However, the authors acknowledged that what this means for patients is unclear.
Alternatives to paracetamol
Where, then, does this leave patients with low back pain or osteoarthritis?
Non-steroidal anti-inflammatory drugs (NSAIDs) such as ibuprofen and naproxen have been found effective for both these conditions, though for many people they're not a suitable option due to the gastrointestinal side effects (stomach ulcers and bleeding) and interactions with other medicines – which tends to preclude older adults who suffer disproportionately from OA and low back pain. They may be suitable for short-term relief, though it's best to ask for your doctor's advice. Topical NSAIDs are better tolerated than oral ones, and are effective for knee osteoarthritis.
Opioids, such as codeine and oxycodone, are other alternatives, but are highly addictive and should only be used short-term for severe pain.
A better course of action – at least as a first line of treatment – involves non-pharmaceutical options for pain relief. These include exercise, as directed by a physiotherapist or exercise physiologist, and weight loss if you're overweight. Manual therapies, massage and heat packs are helpful for back pain, and heat and cold packs for osteoarthritis.
What now for paracetamol?
Experts are calling for a review of paracetamol guidelines for treating osteoarthritis. To date, despite the lack of evidence for the effectiveness of paracetamol, they remain in clinical guidelines as a first line of treatment, partly because the pharmaceutical alternatives – NSAIDs and opioids – have significant side effects and are not a long-term proposition.
On the other hand, paracetamol may also have long-term safety issues. A recent review suggested there are potential cardiovascular, kidney and gastrointestinal effects, and increased risk of all-cause mortality. However, this review was based on observational studies rather than clinical trials, so the findings are less reliable.
Osteoarthritis expert Professor David Hunter, of the University of Sydney, said: "Clinicians should carefully weigh benefits and harms when making treatment decisions. Paracetamol is not efficacious and potentially harmful. In this context we cannot justify its continued use for these prevalent diseases."